/* 地图 */
#map {
    position: relative;
    margin: 0 auto;
    width: 900px;
    height: 600px;
    background-color: #1f575c;
    box-shadow: 0px 0px 50px 20px green;
   }
   /* 蛇头、蛇身体、食物基本样式 */
   .snake-head,
   .snake-body,
   .food {
      position: absolute;
      width: 18px;
      height: 18px;
      border: dotted 1px black;
       border-radius: 17px; 
   }
   /* 蛇的身体 */
   .snake-body {
      background: pink;
   }
   /* 蛇头样式 */
   .snake-head {
      background-color: red;    
   }
   /* 食物 */
   .food {
      background-color: #00ff00;    
   }
   